The present invention relates to a resin composition for a sliding member, and a sliding member produced from the resin composition, and more particularly, to a resin composition suitable for producing a sliding member capable of exhibiting a stable low friction coefficient and an extremely low wear amount under dry frictional condition, or under oil-immersed or oil-lubricated condition, and a sliding member capable of exhibiting a stable low friction coefficient and an extremely low wear amount under dry frictional condition, or under oil-immersed or oil-lubricated condition, which is produced from such a resin composition.
Hitherto, since polytetrafluoroethylene resins (hereinafter simply referred to as xe2x80x9cPTFE resinxe2x80x9d) have not only excellent self-lubricating properties and low friction coefficient, but also chemical resistance and heat resistance, these resins have been used generally for sliding members such as bearings.
However, since the sliding member made of the PTFE resin solely is poor in the wear resistance and load carrying capacity, such a drawback is compensated, for example, by (a) incorporating a solid lubricant such as graphite and molybdenum disulfide, and/or a reinforcing material such as glass fibers and carbon fibers into the PTFE resin, (b) filling the PTFE resin in the pores of a porous sintered metal layer lined by a steel backing plate and coating the surface of the sintered metal layer therewith, or (c) filling the PTFE resin in the meshes of a metal mesh and coating the surface of the metal mesh therewith, depending on the applications of the sliding member.
The sliding members formed by the method (b) have been known as a so-called multi-layered sliding member, and described, for example, in U.S. Pat. No. 2,689,380 (1954) and Japanese Patent Publications (KOKOKU) No. 31-2452(1956), No. 39-16950(1964) and No. 41-1868(1966). The multi-layered sliding members described in these publications have been produced by filling the PTFE resin or the PTFE resin containing a filler composed of lead or a lead oxide in the pores of a porous sintered metal layer lined by a steel backing plate, and coating the surface of the sintered metal layer therewith.
The sliding members formed by the method (c) are described, for example, in Japanese Patent Publication (KOKOKU) No. 55-23740(1980). In the publication, there is disclosed as a sliding member a self-lubricating lining foil comprising a metal wire fabric, a fluoro-plastic and a reinforcing material of inorganic fiber.
In the sliding members described above, fillers have been selectively used according to various different working conditions, for example, under dry frictional condition, oil-immersed condition or oil-lubricated condition, but these sliding members fail to fully satisfy requirements under all of the working conditions.
Further, in a PTFE resin composition for sliding member, it has been attempted to use therein fillers for engineering plastics, for example, graphite, molybdenum disulfide or other metal sulfides, metal oxides, or inorganic fibers such as glass fibers and carbon fibers. Although these fillers contribute to the improvement of the wear resistance of the resin layer, the fillers tend to cause such a problem that the use thereof adversely affects the low-friction property inherent to the PTFE resin. In particular, lead have been widely used as a filler in these resins to improve the wear resistance of a sliding layer. However, for secondary reasons such as recent environmental pollution and public nuisance, the use of lead must be avoided.
As a result of the present inventors"" earnest studies, it has been found that by filling in the pores of a porous sintered metal layer formed on a steel backing plate and coating the surface of the sintered metal layer with a resin composition prepared by blending PTFE with a specific amount of barium sulfate, a phosphate, a polyimide resin, a phenol resin-calcined product or a polyphenylenesulfone resin, or by filling in the meshes of a metal mesh and coating the surface of the metal mesh with a resin composition prepared by blending PTFE with a specific amount of barium sulfate, a phosphate, a polyimide resin, a phenol resin-calcined product or a polyphenylene sulfon resin, the obtained sliding member can exhibit excellent friction and wear characteristics under dry frictional condition, or under oil-immersed or oil-lubricated condition. The present invention has been attained based on this finding.
An object of the present invention is to provide a resin composition for a sliding member capable of exhibiting excellent friction and wear characteristics under various different working conditions, i.e., under dry frictional condition, oil-immersed condition or oil-lubricated condition.
An another object of the present invention is to provide a sliding member capable of exhibiting excellent friction and wear characteristics under various different working conditions, i.e., under dry frictional condition, oil-immersed condition or oil-lubricated condition, which are produced using the resin composition.
To accomplish the aims, in a first aspect of the present invention, there is provided a resin composition for a sliding member comprising 5 to 40% by weight of barium sulfate; 1 to 30% by weight of a phosphate; 1 to 10% by weight of at least one selected from the group consisting of a polyimide resin, a phenol resin-calcined product and a polyphenylene sulfone resin; and the balance of a polytetrafluoroethylene resin. In a second aspect of the present invention, there is provided a sliding member comprising:
a substrate comprising a steel backing plate and a porous sintered metal layer formed on said steel backing plate, or comprising a metal mesh; and
a resin composition applied to pores or meshes and a surface of said substrate, comprising 5 to 40% by weight of barium sulfate, 1 to 30% by weight of a phosphate, 1 to 10% by weight of at least one selected from the group consisting of a polyimide resin, a phenol resin-calcined product and a polyphenylene sulfone resin and the balance of a polytetrafluoroethylene resin.